Slow-Wave Coaxial Transmission Line Formed Using CMOS Processes
An integrated circuit structure includes an interconnect structure over a semiconductor substrate and a coaxial transmission line. The coaxial transmission line includes a signal line, a top plate over the signal line and electrically insulated from the signal line, and a bottom plate under the signal line and electrically insulated from the signal line. At least one of the top plate and the bottom plate includes metal strip shields and dielectric strips, with each of the dielectric strips being between two of the metal strip shields. The integrated circuit structure further includes a ground conductor electrically connecting the top plate and the bottom plate. The ground conductor is insulated from the signal line by a dielectric material.
This application relates to the following commonly-assigned U.S. patent applications: patent application Ser. No. 12/135,659, filed Jun. 9, 2008, and entitled “Microstrip Lines with Tunable Characteristic Impedance and Wavelength;” and patent application Ser. No. 12/023,184, filed Jan. 31, 2008, and entitled “Transmitting Radio Frequency Signal in Semiconductor Structure,” which applications are hereby incorporated herein by reference.
TECHNICAL FIELDThis invention relates generally to the fabrication of integrated circuits, and more particularly to coaxial transmission lines fabricated using complementary metal-oxide-semiconductor (CMOS) compatible processes, and even more particularly to coaxial transmission lines having slow-wave features.
BACKGROUNDTransmission lines are important elements in microwave circuit applications. These devices provide the interconnection between active and passive devices of microwave circuits, and are utilized as impedance matching elements as well. A microstrip line is a type of transmission line widely utilized in monolithic microwave integrated circuit (MMIC) applications.
Microstrip lines have a number of advantages when utilized in MMIC applications. First of all, since microstrip lines are formed of conductive planes disposed on substrates, these devices are readily adaptable to the manufacturing process of the integrated circuits. Accordingly, microstrip lines may be integrated on a same substrate with commonly used integrated circuits such as CMOS circuits.
In addition, microstrip lines typically occupy great chip area. For example, the electromagnetic wavelength in SiO2 dielectric material is about 3000 μm at 50 GHz. Accordingly, microstrip line 2, with the requirement that its length L1 needs to be at least a quarter of the wavelength, which is about 750 μm, in order to match network impedance, is area-consuming. With the increasing down-scaling of integrated circuits, the chip-area requirement of the microstrip lines becomes a bottleneck preventing the integration of microwave devices and the integrated circuits adopting complementary metal-oxide-semiconductor (CMOS) devices.
Accordingly, what is needed in the art are transmission lines that may take advantage of the benefits associated with the reduced energy losses while at the same time overcoming the deficiencies of the prior art.
SUMMARY OF THE INVENTIONIn accordance with one aspect of the present invention, an integrated circuit structure includes an interconnect structure over a semiconductor substrate; and a coaxial transmission line. The coaxial transmission line includes a signal line; a top plate over the signal line and electrically insulated from the signal line; and a bottom plate under the signal line and electrically insulated from the signal line. At least one of the top plate and the bottom plate includes metal strip shields and dielectric strips, with each of the dielectric strips being between two of the metal strip shields. The integrated circuit structure further includes a ground conductor electrically connecting the top plate and the bottom plate. The ground conductor is insulated from the signal line by a dielectric material.
In accordance with another aspect of the present invention, an integrated circuit structure includes a semiconductor substrate; and a plurality of dielectric layers over the semiconductor substrate. The plurality of dielectric layers includes a first dielectric layer; a second dielectric layer over the first dielectric layer; and a third dielectric layer under the first dielectric layer. The integrated circuit structure further includes a coaxial transmission line that includes a signal line in the first dielectric layer, a first ground conductor, a second ground conductor, a top plate, and a bottom plate. The first ground conductor is on a first side of, and is electrically insulated from, the signal line. The first ground conductor extends from inside the second dielectric layer into the third dielectric layer. The second ground conductor is on an opposite side of the signal line than the first ground conductor, and extends from inside the second dielectric layer into the third dielectric layer. The top plate is in the second dielectric layer and includes first metal strip shields and first dielectric strips allocated in an alternating pattern. The bottom plate is in the third dielectric layer and including second metal strip shields and second dielectric strips allocated in an alternating pattern. The first metal strip shields and the second metal strip shields electrically connect the first ground conductor and the second ground conductor.
In accordance with yet another aspect of the present invention, an integrated circuit structure includes a coaxial transmission line, which further includes a signal line extending in a first direction; and a ground line encircling the signal line. The ground line includes a top plate including a first plurality of metal strip shields spaced apart from each other; a bottom plate including a second plurality of metal strip shields spaced apart from each other, wherein a lengthwise direction of the first and the second pluralities of metal strip shields is in a second direction substantially perpendicular to the first direction; and a first ground conductor and a second ground conductor on opposite sides of the signal line. Each of the first ground conductor and the second ground conductor interconnects the first plurality of metal strip shields to the second plurality of metal strip shields.
The advantageous features of the present invention include reduced energy loss in coaxial transmission lines, and tunable characteristic impedances. In addition, the formation of the coaxial transmission lines is highly compatible with existing CMOS manufacturing processes.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Since conventional unshielded transmission lines suffer from high-energy loss, coaxial transmission lines were developed for more efficient signal transmission. U.S. patent application Ser. No. 12/023,184, which is incorporated herein by reference, discloses coaxial transmission line 12, as shown in
The manufacturing of coaxial transmission line 12, however, faces process difficulties. Since the length and the width of coaxial transmission line 12 typically have great values, the manufacturing process violates the CMOS design rules. Particularly, the manufacturing of coaxial transmission line 12 involves chemical mechanical polishes (CMPs). However, the great size of the top plate and the bottom plate of ground line 18 causes the well-known micro-loading effect and dishing effect. In addition, the propagation speed of coaxial transmission line 12 is controlled only by the properties of dielectric material 16, and thus it is difficult to tune the characteristic wavelength of coaxial transmission line 12.
To improve the process compatibility of coaxial transmission lines with the CMOS manufacturing processes and to make the characteristic wavelengths adjustable, novel coaxial transmission lines having tunable characteristic impedances and tunable characteristic wavelengths are provided. The variations of the preferred embodiments are then discussed. Throughout the various views and illustrative embodiments of the present invention, like reference numbers are used to designate like elements.
Embodiments of the invention relate to integrated circuits having a coaxial transmission line including at least one ground conductor coupled with a top plate and a bottom plate, at least one of which having metal strip shields and dielectric strips, each dielectric strip between two of the metal strip shields. The coaxial transmission line can provide tunable characteristic impedances and/or slow-wave features by adjusting widths and spacings of the metal strip shields.
Referring to
Referring to
Strip lengths SL of different strip shields 241 preferably have a periodic pattern, that is, neighboring strip shields 241 may be grouped, with strip lengths SL of strip shields 241 in one group repeating the width pattern in other groups. In each of the groups, the strip lengths SL may be arranged in an order from smaller to greater (for example, forming an arithmetic sequence or a geometric sequence), with each of strip lengths SL being greater than a previous one. More preferably, in each of the top plate and the bottom plate of ground line 24, all of strip shields 241 preferably have a same strip length SL, although strip lengths SL may also be different from each other. Similarly, all spacings SS between neighboring strip shields 241 are preferably equal to each other. Alternatively, spacings SS may have other periodic patterns similar to that of strip lengths SL.
The formation methods of signal line 22 and ground line 24 may include commonly known single and dual damascene processes, wherein signal line 22 and ground line 24 are formed of copper or copper alloys. Accordingly, signal line 22 may include only a metal line portion, but not a via portion. Alternatively, as shown in
Referring to
In coaxial transmission lines that have solid ground planes, the signal return path is mostly in the top plate and the bottom plate, and at positions directly overlying and underlying the respective signal line. Advantageously, in the embodiments of the present invention, dielectric strips 36 (refer to
The embodiments of the present invention have several advantageous features. First, the characteristic impedances and characteristic wavelengths may be tuned by adjusting the distances between ground conductors. Second, by forming periodical, instead of solid, top plate and bottom plate, the formation of the coaxial transmission lines is now fully compatible with the formation processes of CMOS circuits. The formation of the embodiments of the present invention do not need additional masks, and hence the manufacturing cost is not increased.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Claims
1. An integrated circuit structure comprising:
- a semiconductor substrate;
- an interconnect structure over the semiconductor substrate; and
- a coaxial transmission line comprising: a signal line; a top plate over the signal line and electrically insulated from the signal line; a bottom plate under the signal line and electrically insulated from the signal line, wherein at least one of the top plate and the bottom plate comprises: metal strip shields; and dielectric strips, each between two of the metal strip shields; and a first ground conductor electrically connecting the top plate and the bottom plate, wherein the first ground conductor is insulated from the signal line by a dielectric material.
2. The integrated circuit structure of claim 1 further comprising a second ground conductor electrically connecting the top plate and the bottom plate, wherein the second ground conductor is on an opposite side of the signal line than the first ground conductor.
3. The integrated circuit structure of claim 1, wherein both the top plate and the bottom plate comprise the metal strip shields and the dielectric strips.
4. The integrated circuit structure of claim 1, wherein the metal strip shields and the dielectric strips have widths substantially equal to a minimum dimension of the integrated circuit structure.
5. The integrated circuit structure of claim 1, wherein the first ground conductor extends into a plurality of dielectric layers, and wherein in each of the plurality of dielectric layers, the first ground conductor comprises a metal line portion and a via portion forming a solid vertical metal wall.
6. The integrated circuit structure of claim 1, wherein the first ground conductor extends into a plurality of dielectric layers, wherein in each of the plurality of dielectric layers, the first ground conductor comprises a metal line portion and a plurality of vias underlying and contacting the metal line portion, and wherein the plurality of vias is separated from each other by dielectric regions.
7. The integrated circuit structure of claim 1, wherein the metal strip shields have lengthwise directions substantially perpendicular to a lengthwise direction of the signal line.
8. An integrated circuit structure comprising:
- a semiconductor substrate;
- a plurality of dielectric layers over the semiconductor substrate, the plurality of dielectric layers comprising: a first dielectric layer; a second dielectric layer over the first dielectric layer; and a third dielectric layer under the first dielectric layer; and
- a coaxial transmission line comprising: a signal line in the first dielectric layer; a first ground conductor on a first side of, and electrically insulated from, the signal line, wherein the first ground conductor extends from inside the second dielectric layer into the third dielectric layer; a second ground conductor on an opposite side of the signal line than the first ground conductor, wherein the second ground conductor extends from inside the second dielectric layer into the third dielectric layer; a top plate in the second dielectric layer and comprising first metal strip shields and first dielectric strips allocated in an alternating pattern; and a bottom plate in the third dielectric layer and comprising second metal strip shields and second dielectric strips allocated in an alternating pattern, wherein the first metal strip shields and the second metal strip shields electrically connect the first ground conductor and the second ground conductor.
9. The integrated circuit structure of claim 8, wherein each of the first ground conductor and the second ground conductor is in a form of a solid wall with no opening therein.
10. The integrated circuit structure of claim 8, wherein each of the first ground conductor and the second ground conductor comprises a metal line portion, and a plurality of via columns under the metal line portion.
11. The integrated circuit structure of claim 8, wherein the first metal strip shields and the second metal strip shields have substantially a same width.
12. The integrated circuit structure of claim 8, wherein widths of the first metal strip shields and the second metal strip shields have a periodic pattern, and wherein neighboring ones of the first metal strip shields and the second metal strip shields have different widths.
13. The integrated circuit structure of claim 8, wherein the first dielectric strips and the second dielectric strips have substantially a same width.
14. The integrated circuit structure of claim 8, wherein widths of the first dielectric strips and the second dielectric strips have a periodic pattern, and wherein neighboring ones of the first dielectric strips and the second dielectric strips have different widths.
15. The integrated circuit structure of claim 8, wherein the first metal strip shields and the second metal strip shields have lengthwise directions substantially perpendicular to a lengthwise direction of the signal line.
16. An integrated circuit structure comprising:
- a coaxial transmission line comprising: a signal line extending in a first direction; and a ground line encircling the signal line, wherein the ground line comprises: a top plate comprising a first plurality of metal strip shields spaced apart from each other; a bottom plate comprising a second plurality of metal strip shields spaced apart from each other, wherein a lengthwise direction of the first and the second pluralities of metal strip shields is in a second direction substantially perpendicular to the first direction; and a first ground conductor and a second ground conductor on opposite sides of the signal line, wherein each of the first ground conductor and the second ground conductor interconnects the first plurality of metal strip shields to the second plurality of metal strip shields.
17. The integrated circuit structure of claim 16, wherein the coaxial transmission line extends into a first metal layer and a second metal layer, and wherein the first metal layer and the second metal layer comprise different dielectric materials.
18. The integrated circuit structure of claim 16, wherein the first plurality of metal strip shields and the second plurality of metal strip shields have a same width.
19. The integrated circuit structure of claim 16 further comprising dielectric materials filling first spacings between the first plurality of metal strip shields and second spacings between the second plurality of metal strip shields.
20. The integrated circuit structure of claim 16, wherein each of the first plurality of metal strip shields and the second plurality of metal strip shields has a minimum width allowed by a forming technology of the integrated circuit.
Type: Application
Filed: Dec 9, 2008
Publication Date: Jun 10, 2010
Patent Grant number: 8279025
Inventor: Shu-Ying Cho (Hsin-Chu)
Application Number: 12/331,090
International Classification: H01P 1/18 (20060101);